Head-mounted displays for computer systems position computer-generated visual information close to a user's eyes. Many head-mounted displays use a translucent display or only partially cover the user's field of vision, allowing computer information to overlay the user's normal vision. Such head-mounted displays typically provide informational overlays, which may respond to the user's current context. Head-mounted displays may render computer-generated visual features that appear to be integrated with the user's environment, also referred to as “augmented reality.” Other head-mounted displays may completely cover the user's field of vision with computer-generated visual features, for example in “virtual reality” applications.
Current head-mounted displays are known to induce nausea in many users. Typically, there is a small amount of latency between the user's head movements and the responsive display of objects on the head-mounted display. For many users, that latency induces motion sickness and/or nausea. Head-mounted displays may also induce nausea by rendering motion that is different from the user's true motion. For example, moving forward in a virtual space while standing still in reality may induce motion sickness and/or nausea. The incidence of nausea may increase with the length of time the head-mounted display is in use.
Additionally, head-mounted displays may increase the risk of seizure in some users. For example, a certain proportion of the population with epilepsy is photosensitive; that is, for some users, exposure to flashing lights or to certain visual patterns may trigger seizures. In particular, flashing lights at a frequency between five and thirty flashes per second is known to trigger seizures in some persons. Even where seizures are not triggered, some photosensitive persons may experience other symptoms such as headache, nausea, or dizziness. Head-mounted displays—like any other display technology—may generate flashes or visual patterns capable of triggering seizures or other physical problems.
Nausea and seizure may be detected in real time by analyzing sensor data that monitors the physiological state of the user. Nausea is known to change the user's skin conductivity (galvanic skin response, or “GSR”), skin temperature, pulse rate, and possibly eye blink rate. Nausea may also be detected through measurement of the user's motor stability. Similarly, seizure may be detected by measuring the user's motor activity for events such as falling or trembling, or through eye gaze tracking.